Robert,
To get into that PLC you would need to find the programming software.... to see what it is doing for you machine. If mach is to control it, you would need
to hook to it via Serial or Ethernet coms, you would need to also find out, if it would take RTU Modbus communications for control.
I am NOT trying to discourage you in any way, but, unless you have the software to see what that PLC is suppossed to do, OR, you have the Electrical CADs that show the Ladder rung program in the PLC. You are kinda screwed.
Looking at your machine you will have to write custom UP/DOWN macros for each spindle head, and possibly 4 individual spindle speed/on/off control macros as well,
and a customized screen set to reflect that. (Look in the Finished Plugins section of this forum, there is a 3 Spindle plugin control I did with screen set that you can download and use to get an idea of what I am talking about).
Realistically: It would probably be better for you to Pull that PLC and sell it on Ebay, and Get you some other PLC (Automation Direct etc.), that you would have better control over. Unless you can find the programming software for that PLC and add a communication module to talk to Mach3.
You would also need to consider the IO for the: Vacuum system (if it has one), Tool changing (ATC if it has one), external physical button controls.
The CAM that you use will need to be able to post out the M codes that represent the state of your router heads......
scott